The present invention relates to an improved edged medical tool, such as injection needles, knives, scalpels, scissors, chisels and the like, used in medical and dental treatments and surgical operations for therapeutic, preventive and examination purposes, and a method for the preparation of such an improved edged medical tool.
The above mentioned edged medical tools are used for incising or cutting a living body tissue or for injecting a liquid medicament into or taking a body fluid from a living body so that it is essentially important that the edge of the tool can be thrusted into the living body tissue with a frictional resistance as small as possible. Further, it is important that the surface of the tool in contact with the living body tissue is not responsible for accelerated coagulation of blood and is stable against and insusceptible to the corrosive influence of the body fluids even when the tool is prolongedly kept in contact with the living body tissue. Needless to say, the edge of the tool should be as sharp and incisive as possible like other edged tools in general.
Conventionally, these edged medical tools are manufactured of a ceramic material or a metal optionally coated with a ceramic. The edged medical tools prepared from these prior art materials are not quite satisfactory in respect of the high frictional resistance in thrusting into living body tissues and acceleration of blood coagulation. Accordingly, it is eagerly desired in the medical and dental art to develop an edged tool free from the above mentioned problems in the conventional edged tools and satisfying the above mentioned requirements.
One of the inventors previously disclosed in Japanese Patent Kokai No. 61-210179 that the performance of a microtome blade such as incisiveness could be remarkably improved by forming a coating layer of silicon carbide on the surface of a substrate blade by the plasma-induced vapor-phase deposition method. Such a method of coating with silicon carbide, however, is not quite effective when a substantial improvement is desired of an edged medical tool. Further, it is disclosed in Japanese Patent Kokai No. 63-92345 that a substantial improvement can be obtained in the performance of an edged medical tool when the surface of the edged tool is provided with a carbonaceous coating layer of a diamond-like crystalline structure having a thickness of 1 to 20 nm which is deposited by the plasma-induced vapor-phase deposition in an atmosphere of a gaseous mixture of hydrogen and a hydrocarbon compound such as methane. The diamond-coated edged medical tool, however, is still not quite satisfactory when the tool is used in a very exquisite technique of so-called microsurgery applied to an extremely minute portion of a living body in respect of the damage to the living cells.